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Quality control (QC) detects changes in the performance of gamma cameras that could adversely affect interpretations of clinical studies. We used plate and sheet (57)Co flood sources to measure extrinsic uniformity during daily QC. Each source, when placed on the top of a collimated detector, allowed the acquisition of uniform images from both detectors, thus reducing the amount of time needed to perform daily QC. No serious problems with the gamma camera system were revealed by visual checks, and changes in detector sensitivity were rapidly determined by observing daily variations in the measured values of extrinsic uniformity. Furthermore, (57)Co flood sources confer advantages in that they shorten the time required for preparation of flood sources and reduce the consequent exposure of medical staff to radiation.

By sodium nickel ferrocyanide coprecipitation, 60Co and 137Cs are simultaneously collected by nearly 99% recoveries from the unaged seawater. But this coprecipitation is not effective for the recovery of the 60Co complexed with organic ligands which would exist in natural seawater. In order to obtain the effective recoveries for these complexed 60Co, various pretreatments were investigated by using model samples containing the 60Co aged with several amino acids. In the acidification of these samples by nitric acid as 1 pretreatment, a large portion of these complexed 60Co was dissociated, especially by heating samples at 90-95 degrees C. The recoveries of 60Co were ranging from 90 to 97%. On the other hand, the usage of potassium peroxodisulfate (4.0 x 10(-4)-2.0 x 10(-2) M) as another pretreatment method elevated the recoveries of these complexed 60Co by more than 99% by heating samples above 90 degrees C. These 2 pretreatment methods were also effective for recoveries of 137Cs ion.

The concentration of 60Co and stable cobalt in the shellfishes and seaweeds which were collected from the coast around Japan were obtained by low background beta counting for 60Co and spectrometric determination of stable cobalt. The results obtained were as follows: (1) The 60Co was found in the shellfishes which were enriched in the stable cobalt. (2) The correlation between 60Co and stable cobalt was rather good in the shellfishes. (3) The activities of 60Co was found in the seaweeds taken from seashore near the nuclear power plant. (4) There was great differences in the specific activities between samples collected from contaminated and not contaminated area.

Studies were made to develop the method for rapid determination of radioactive and stable cobalt in a single specimen of marine biological materials. The sample was dried, ashed, and dissolved in acid. The cobalt was extracted with 1-nitroso-2-naphthol benzene and determined by absorptiometry on the benzene phase. Then, the organic solution was evaporated to dryness, and the residue was treated with nitric-perchloric acid mixture to decompose any organic matter, and taken up with hydrochloric acid. The cobolt was extracted from the solution with TIO A-toluene, and the radioactive cobalt was determined by liquid scintillation counting on the toluene phase. Examinations were made on the chemical yield and on the decontamination factor of the fission product nuclides. Analysis were made on the marine biological samples of Urazoko Bay, Fukui prefecture. Agreement of the radioactive cobalt data between that by the present method and that by Ge(Li) gamma ray spectometry was good. Also, the stable cobalt value by the present method agreed well with that by neutron activation analysis method.

Two kinds of mussel, Septifer virgatus and Mytilus edulis, were collected from Kyushu island, Japan, in order to elucidate a background level of 60Co, which is one of the most significant radionuclide for environmental monitoring around a nuclear power plant. The mussels were collected from 7 locations in 1983 and classified 2 or 3 groups depending on their shell size at each location. Activities of 60Co were measured by a low-background beta counter after purified by means of chemical separation and electrodeposition. Stable cobalt concentrations were determined by colorimetric method. The concentrations of cobalt in Septifer virgatus are one order higher level than that in Mytilus edulis. There are not so large difference in cobalt content depending on shell size so long as comparing them at the same location. The radioactivities in mussels show the same trend as stable cobalt. It has become apparent that Septifer virgatus has a tendency to concentrate cobalt with growing but Mytilus edulis is opposite. The cobalt-60 introduced to sea from nuclear explosions seems to be relatively constant in coastal seawater since specific activities are distributed in a narrow range in spite of kind, shell size and location.

In order to investigate both the contamination level and distribution of radioactive nuclides in the marine environment, the concentrations of both 60Co and stable cobalt were determined. The samples collected from the sea around Japan were fishes, squids. The analytical method for 60Co was consisted of the radiochemical separation using ion exchange resins followed with the low background beta counting, and that for stable cobalt was the spectrophotometric determination. The results obtained were as follows: (1) The viscera of squids was found to enrich both 60Co and stable cobalt. (2) No 60Co was detected in fishes except the liver of bonito taken from the north west Pacific. (3) The correlation between 60Co and stable cobalt was rather good in the squids samples. (4) The enrichment factors for squids and fishes agreed well with the values reported by B. Patel or S.E. Tompson.